Generally a hearing aid system may be any system which provides an output signal that can be perceived as an acoustic signal by a user or contributes to providing such an output signal, and which has means which are used to compensate for an individual hearing loss of the user or contribute to compensating for the hearing loss of the user or contribute to compensating for the hearing loss. These systems may comprise hearing aids which can be worn on the body or on the head, in particular on or in the ear, and can be fully or partially implanted. However, some devices whose main aim is not to compensate for a hearing loss, may also be regarded as hearing aid systems, for example consumer electronic devices (televisions, hi-fi systems, mobile phones, MP3 players etc.) provided they have, however, measures for compensating for an individual hearing loss.
Within the present context a hearing aid may be understood as a small microelectronic device designed to be worn behind or in the human ear by a hearing-impaired user. The hearing aid may be powered by a battery or some other energy source. Prior to use, the hearing aid is adjusted by a hearing aid fitter according to a prescription. The prescription is based on a hearing test, resulting in a so-called audiogram, of the performance of the hearing-impaired user's unaided hearing. The prescription is developed to reach a setting where the hearing aid will alleviate a hearing loss by amplifying sound at frequencies in those parts of the audible frequency range where the user suffers a hearing deficit. A hearing aid comprises one or more microphones, a battery, a microelectronic circuit comprising a signal processor, and an acoustic output transducer. The signal processor is preferably a digital signal processor. The hearing aid is enclosed in a casing suitable for fitting behind or in a human ear. For this type of traditional hearing aids the mechanical design has developed into a number of general categories. As the name suggests, Behind-The-Ear (BTE) hearing aids are worn behind the ear. To be more precise, an electronics unit comprising a housing containing the major electronics parts thereof is worn behind the ear, and an earpiece for emitting sound to the hearing aid user is worn in the ear, e.g. in the concha or the ear canal. In a traditional BTE hearing aid, a sound tube is used to convey sound from the output transducer, which in hearing aid terminology is normally referred to as the receiver, located in the housing of the electronics unit and to the ear canal. In some modern types of hearing aids a conducting member comprising electrical conductors conveys an electric signal from the housing and to a receiver placed in the earpiece in the ear. Such hearing aids are commonly referred to as Receiver-In-The-Ear (RITE) hearing aids. In a specific type of RITE hearing aids the receiver is placed inside the ear canal. This category is sometimes referred to as Receiver-In-Canal (RIC) hearing aids. It has been suggested to design RITE or RIC hearing aids, wherein only the ear parts comprise at least one microphone. Another category of hearing aids is characterized in that at least one microphone is arranged in each of a behind the ear part and an earpiece part. In-The-Ear (ITE) hearing aids are designed for arrangement in the ear, normally in the funnel-shaped outer part of the ear canal. In a specific type of ITE hearing aids the hearing aid is placed substantially inside the ear canal. This category is sometimes referred to as Completely-In-Canal (CIC) hearing aids. This type of hearing aid requires an especially compact design in order to allow it to be arranged in the ear canal, while accommodating the components necessary for operation of the hearing aid.
Generally a hearing aid system may comprise a single hearing aid (a so called monaural hearing aid system) or comprise two hearing aids, one for each ear of the hearing aid user (a so called binaural hearing aid system). Furthermore the hearing aid system may comprise an external device, such as a smart phone having software applications adapted to interact with the other devices of the hearing aid system.
It is well known within the art of hearing aid systems that so called binaural cues are important in order to understand speech in noisy environments. Inter-aural Level Difference (ILD) is one type of binaural cue and Inter-aural Time Difference (ITD) is another.
In the article “Better-ear glimpsing at low frequencies in normal-hearing and hearing-impaired listener”, by Rana and Buchholz, published in J. Acoust. Soc. Am. 140 (2), August 2016, pages 1192-1205, it is shown that artificially generated ILDs at low frequencies may improve speech understanding in noise. The article suggests that artificially created ILDs may be provided by directional hearing aid microphones, but also states that neither the optimal directivity nor the required number and placement of microphones to achieve the optimal directivity is known.
It is well known within the art of hearing aid systems to provide hearing aids with directional capabilities. Normally this is achieved by using two or more microphones to permit the hearing aid to process incoming sounds according to direction of incidence in order to achieve increased sensitivity towards sound coming from a particular direction, or range of directions. In this process the hearing aid relies on differences in arrival time and sound level among the microphones. A hearing aid with a directional capability allows a hearing aid user to perceive a sound coming from a particular direction, while sounds from other directions are suppressed to some extent. This may be useful to improve speech perception in noisy environments, especially environments where human speech may be received simultaneously from different directions, as is the case e.g. in the sound environment frequently referred to as cocktail party. With a directional sound receiving characteristic, e.g., in the shape of a cardioid or hypercardioid characteristic, the speech intelligibility for the hearing aid user is improved by reduced perception of sound coming from the back and the sides of the user while maintaining the level of sound coming from the area in front of the user, where it is assumed that the desired speaker is located.
Normally the term “directivity” is used to signify the capability of a hearing aid to favor sound originating from a particular direction or range of directions over sound originating from other directions. Physically, the definition of hearing aid directivity is the ratio between the output level due to sound from the favored direction and the output level due to sound averaged over the integral from all other directions, typically expressed in dB.
WO 01/01731-A1 discloses a method for controlling the directional characteristic of a hearing aid. The directional characteristic may be created by adjusting a delay in the signal processor to be the same as the acoustical delay between the back microphone and the front microphone, whereby signals that are first received at the back microphone and later received at the front microphone, after having propagated along the line between the front and back microphones, may be suppressed.
It is a feature of the present invention to provide a method of operating a binaural hearing aid system that increases the ILD.
It is another feature of the present invention to provide a binaural hearing aid system adapted to provide increased ILD.